Even-toed ungulates
The even-toed ungulates (Artiodactyla, Greek ἄρτιος (ártios), meaning 'even', and δάκτυλος (dáktylos), meaning 'finger / toe') are s – hoofed animals – which bear weight equally on two (an even number) of the five toes: their third and fourth toes. The other three toes are either present, absent, , or pointing posteriorly. By contrast, s bear weight on one (an odd number) of the five toes: the third toe. Another difference between the two is that even-toed ungulates digest plant in one or more chambers rather than in their as the odd-toed ungulates do. The aquatic ns ( s, dolphins, and porpoises) evolved from even-toed ungulates, so modern taxonomic classification sometimes combines the Artiodactyla and Cetacea into the Cetartiodactyla. The roughly 220 land-based even-toed ungulate species include s, , es, s, s, s, , , s, s, , s, and . Many of these are of great dietary, economic, and cultural importance to humans. Evolutionary history s were stocky animals with a large head, and were characterized by bony bumps on the lower jaw.|alt=Two large boar-like creatures graze.}} '' was a relative of giraffes with deer-like forehead weapons.|alt=A deer-like animal wanders through a clearing.}} The oldest fossils of even-toed ungulates date back to the early (about 53 million years ago). Since these findings almost simultaneously appeared in Europe, Asia, and North America, it is very difficult to accurately determine the origin of artiodactyls. The fossils are classified as belonging to the family ; their best-known and best-preserved member is . These were small animals, some as small as a , with a slim build, lanky legs, and a long tail. Their hind legs were much longer than their front legs. The to middle Eocene saw the emergence of the ancestors of most of today's mammals. Two formerly widespread, but now extinct, families of even-toed ungulates were and . Entelodonts existed from the middle Eocene to the in and North America. They had a stocky body with short legs and a massive head, which was characterized by two humps on the lower jaw bone. Anthracotheres had a large, (pig-like) build, with short legs and an elongated . This group appeared in the middle Eocene up until the , and spread throughout Eurasia, Africa, and North America. Anthracotheres are thought to be the ancestors of hippos, and, likewise, probably led a similar aquatic lifestyle. Hippopotamuses appeared in the and occupied Africa and Asia – they never got to the Americas. The camels ( ) were, during large parts of the , limited to North America; early forms like occupied Europe. Among the North American camels were groups like the stocky, short-legged . They first appeared in the late Eocene and developed a great diversity of species in North America. Only in the late Miocene or early Pliocene did they migrate from North America into Eurasia. The became extinct around 10,000 years ago. (including s) have been around since the Eocene. In the late Eocene or the , two families stayed in Eurasia and Africa; the , which became extinct in the , exist today only in the . South America was only in the Pliocene, after the at the formed some three million years ago. With only the peccaries, lamoids (or s), and various species of , South America has than other continents, except Australia, which has no native species. Phylogenetic tree |1= (camels) |label2= |2= (pigs) |label2= |2= (ruminants) |1= (mouse deer) |2= (horn bearers) }} |label2= / |2= (hippopotamuses) |2= (whales) }} }} }} }} }} References Category:Tree of life